1. Field of the Invention
The invention relates to the field of X-ray imaging equipment for producing a projection image on radiographic film or a reusable phosphor plate in combination with the moving tabletop of a computer tomography X-ray scanner.
2. Description of the Prior Art
Analog radiography is a method by which projection X-ray images of the human body or other object are recorded on X-ray film or some other photosensitive surface. Analog radiology is known to provide excellent spatial resolution, but poor contrast resolution.
Computerized radiography is a method by which projection X-ray images the human body or other objects are obtained by recording a latent image on a storage reusable phosphor plate which is then read under computer control by an interrogating light beam. The phosphor emits light of another wavelength which is proportional to the intensity of the X-ray. The emitted signal is digitized and displayed on a cathode ray tube monitor or laser printed on film or other media. Computerized radiography provides moderate spatial resolution and moderate contrast resolution which is improved over the contrast resolution realized by analog radiography.
Computer tomography is a method by which the cross sectional images of a human body or other objects is obtained by rotating an X-ray tube and an opposing array of X-ray detectors about the human body or object. The collimated X-ray beam fans out laterally while it is narrowly collimated along its longitudinal axis. Computer tomography provides poor spatial resolution, but excellent contrast resolution.
A very crude, low resolution projection image may also be obtained in a computer tomographic scanner by moving the object or human body through a collimated fanned beam and detector array. This is obtained by providing linearly moving the patient or object on a motorized tabletop on through a stationary collimated fan beam.
Conventional slot analog radiography is also known. The procedure is to expose the patient with a collimated fan X-ray beam. Behind the patient is an X-ray barrier with a conforming slot defined through it. The collimated beam and its slotted barrier are moved in unison down the length of the patient as the patient stands between the two. Positioned behind the slotted X-ray barrier is a stationary film plate. The film plate is fixed relative to the patient and receives the projection X-ray image from the patient as the slotted barrier moves across it. The results are comparable to analog radiography, the only difference being that the patient is sequentially exposed to a collimated beam of X-rays as opposed to having an entire area simultaneously exposed to a shaped beam. The contrasting resolution obtainable by conventional slot radiography remains poor although the spatial resolution of the projection radiographs are good.
Analog radiography and computerized radiography use traditional radiographic equipment whose fundamental technology has been substantially unchanged over the last 100 years. Computer tomography employs a radically different geometric design comprised of a gantry and motorized tabletop. In most if not all fully equipped radiology clinics and hospitals, one set of equipment is provided to produce high spatial resolution radiographs and another set of equipment to produce high contrast resolution axial radiographs. Hundreds of thousands of such units of each kind are used throughout the world. The cost of each of these units is substantial and currently both types of units are required to fully meet current standards of radiological practice.
Therefore, what is needed is a single apparatus and methodology or some means by which existing radiographic equipment can be modified or used which would provide both the excellent spatial resolution of analog radiography while at the same time providing the high contrast resolution of computer tomography without the need to provide expensive duplicate sets of radiographic instrumentation.